Having pulled a shocking upset, the winning candidate is, well, shocked. “What do we do now?” he asks his handler.

The question is left hanging in the 1972 movie “The Candidate,” where Robert Redford plays a politician who, never expecting to win, had given no thought to governing.

I suspect Bill de Blasio is familiar with the terrifying feeling.

Polls show the Democrat with a huge lead, but his weak performance at last night’s mayoral debate should spark buyers’ remorse among supporters. He gave incoherent and at times dishonest answers about the most important issues facing New York, raising fresh doubts about whether de Blasio is ready for the job.

Republican Joe Lhota, on the other hand, passed crucial tests about his own convictions and qualifications. The punch-pulling hesitancy he showed in last week’s debate was gone, replaced with a forceful vision for keeping the city safe and supporting parental choice on schools. And befitting his underdog status, he repeatedly took the fight to de Blasio.

As a result, the contrasts on key issues were stark. And despite de Blasio’s attempts to fudge his attacks on the NYPD, the veneer came off to reveal a thin skin and a nasty habit of making wild charges.

Pressed by Lhota about his work for David Dinkins during the Crown Heights anti-Semitic riots 22 years ago, de Blasio quickly reached for the race card. He called Lhota’s ad on the Dinkins years “race baiting and fear mongering” only a few minutes after urging Lhota “to not use incendiary terms.”

He also alternately praised the NYPD and accused it of racial profiling and spying on Muslims, then said the department should use “overwhelming force” in riots. Wanting it both ways made him look casually conniving and lacking conviction, a charge his primary opponents often made.

The excellent moderator, Channel 2 anchor Maurice DuBois, began by zeroing in on crime, and kept coming back to it.

He asked de Blasio about the fact that the public, by 62 percent to 30 in a Quinnipiac poll, thinks keeping crime low is more important than reforming stop-and-frisk. It’s an important distinction because many of de Blasio’s supporters don’t support big parts of his agenda. The gap could mean victory would come with a short leash and not much of a mandate.

That should alarm de Blasio, who barely mentions crime itself, leaving the impression he sees cops as more of a problem than criminals. Similarly, another poll found 62 percent want Ray Kelly to remain police commissioner, even as de Blasio says he will fire him.

The pattern is clear: After 20 years of falling crime, New Yorkers have come to expect safe streets, and woe is the mayor who allows murder to make a comeback.

That concern is Lhota’s strong suit and he played it well. He credited his former boss Rudy Giuliani with starting “the renaissance” in New York, a point he shied away from in the first debate. And when de Blasio accused Giuliani of being “divisive,” Lhota made the same charge of Dinkins and said that’s why he was fired after one term. Touché.

The exchange highlighted my belief that this election, featuring loyalists from both camps, is something of a referendum on the last 20 years. On facts alone, Lhota has the upper hand and is better prepared to be mayor.

But de Blasio is an experienced politician who, although he won the primary with only 40 percent, inherits the Dems’ 6-1 registration advantage. After 20 years of being shut out of City Hall, the party is hungry for power and patronage. De Blasio stokes that appetite by sneering that Lhota is a Republican.

All’s fair in politics, but only in Hollywood can the winner escape the question of how he will govern. If the polls hold, de Blasio will have to face the music, ready or not.

OMG! He’s sliding fast

This just in: Team Obama has changed its rallying cry of “Yes We Can” to “No We Can’t.”

Can’t do anything right, that is.

The second term is only 10 months old, but it feels like a decade of failure. It’s been all downhill since the inauguration, and the rollout of ObamaCare suggests things will get worse before they get better. Much worse.

Even Obama’s skill — making speeches before adoring crowds — is a punch line, thanks to Monday’s dreary infomercial. Jon Stewart, who usually reserves his barbs for Republicans, mocked the president’s performance in ways that had to warm Ted Cruz’s heart. When Dems lose Stewart, they’re in deep doo-doo.

The comedian better have paid his taxes. This White House is not shy about using the IRS to enforce loyalty. And Consumer Reports should look over its shoulder after telling readers to “stay away” from the ObamaCare site until it is fixed.

The computer problems are just the start. The law is a variation on a Ponzi scheme in that it relies on young, healthy new customers to provide insurance companies with the money to pay for treating older, sicker ones.

Because of sweeping dictates on coverage, many potential buyers will face sticker shock. Some will choose to pay a fine instead, further pushing up the cost for those who enroll.

For others, including people in private plans, the law’s impact on premiums, deductibles and co-pays will drive up, not down, the cost of care.

Then there is the cost for the bureaucratic army needed to take over one-sixth of the economy. The expensive tech “surge” Obama promises will add to the estimated $400 million spent on the computer system alone.

All that explains why ObamaCare is his “signature” achievement. It perfectly reflects his arrogance and incompetence.

Hardly taken by $torm

The package passed after Jersey Gov. Chris Christie and New York Congressmen Michael Grimm and Peter King blasted fellow Republicans for initially blocking it. They declared the matter a life-or-death emergency.

Or maybe it wasn’t, since the bureaucracy is still sitting on the cash. Where’s the outrage?

New Rangel sleaze play

A new muckraking book on Congress says Harlem Rep. Charlie Rangel spent $64,500 on a painting of himself.